Communication system networks are known to comprise a plurality of communication systems and a central controller. Each of the communication systems comprises a plurality of communication units, a limited number of communication resources that are transceived via a limited number of repeaters, and a communication resource allocator that allocates the communication resources among the plurality of communication units. The communication units, which may be mobile radios, portable radios, and/or portable radio/telephones, are typically arranged in to communication groups and are generally located throughout the communication system network. Of the communication resources, which may be TDM slot locations, frequency carriers, pair of frequency carriers, or any other RF transmission means, one is selected to function as a control channel. The control channel transceives operational information between the communication units and the central controller via the communication resource allocators.
As is known, a communication unit may establish a communication with other communication units within the communication system network by transmitting an inbound signalling word (ISW) to the central controller via the communication resource allocator of the communication system that the communication unit is located in. Upon receiving the request, the central controller processes it and, if the request is valid, the central controller allocates a communication resource in each of the communication systems that have a communication unit of the targeted talk group in it. The communication systems, which may also be communication sites, are coupled to and controlled by the central controller. If a communication system, or site, loses contact with the central controller, the communication system, or site, operates as an independent communication system but only for communication units that are located within its coverage area.
As is also known, under certain circumstances, a communication group that does not normally communicate with another communication group may be combined such that the separate communication groups act as one. For example, in an emergency condition, the police communication group and the fire communication group may be combined into one to respond to a particular emergency. To process this, the central controller, when the emergency condition is initiated by a communication unit in either the police or the fire department communication group, allocates a communication resource in each of the communication systems, or sites, for the combined group. This type of broad regrouping may be inefficient when the particular emergency is occurring in a very localized area. For example, members of the fire department and police department may be located anywhere within the communication system network and be several tens of miles away from the area where the emergency is occurring. Thus, notifying these members of the combined communication group is unnecessary because these members are physically unable to respond to the emergency condition. Therefore, a need exists for a method that will allow the central controller to expand the audience, or regroup communication groups, to respond to predetermined communications but only in selected communication systems.